The present invention provides methods and compositions for the diagnosis, monitoring, and modulation of the immune response to Hepatitis C Virus (HCV) related diseases. The methods take advantage of a novel reactive mechanism of the murine monoclonal antibody (mAb) 1F7 against human antibodies specific for different proteins of the Hepatitis C virus (HCV). In particular, the antibodies recognize HCV core protein in a majority of HCV-infected individuals and antibodies against HCV non-structural proteins 3 (NS3) and NS4 in some HCV-infected individuals. Also, the antiidiotypic antibody recognizes antibodies against the putative principle neutralizing determinant (hypervariable region 1 of the HCV E2 protein) of HCV. The idiotypic linking of antibodies against multiple epitopes of a chronic pathogen provides methods for improved diagnosis and monitoring of HCV as well as opportunities to increase the efficiency of immune regulation, including limiting “idiotypic “grid-lock”, that can arise from chronic antigenic stimulation.
Hepatitis C virus (HCV) is a plus sense RNA virus that establishes chronic infection in up to 80% of exposed individuals. Long-term infection can lead to liver cirrhosis and hepatocellular carcinoma. Currently, no effective vaccine or treatment for HCV infection is available. The ability of HCV to mutate key immunological determinants and to escape immune selection pressures exerted by antibodies and T cells in an infected individual is important for the establishment of chronic infection. Similar to HLV infection, the immune system can become locked into recognition of the original infecting strain of HCV and therefore is unable to adapt to, and recognize, subsequent mutations. Antibodies against a particular region of HCV E2 protein, hypervariable region 1 (HVR1) are believed to be important to preventing new infection of cells and promoting clearance of viral particles. An antibody response directed against a broad range of HCV epitopes in addition to HCV E2 HVR1 would be expected to provide better protection against HCV mutants and to be associated with a more favorable clinical outcome to infection.
Although HCV and HIV are genetically unrelated and the viruses have a different pattern of cellular tropism and induce distinct diseases, HCV and HIV share important features relevant to their interactions with the immune system of the infected host. In particular, both viruses commonly establish chronic infections, thought at least in part, to be due to RNA polymerases characterized as “mistake-prone” that generate a high mutation rate during viral replication (Bebenek et al., J. Biol. Chem. 264:16948-16956 (1989); Ogata et al., Proc. Natl. Acad. Sci USA 88:3392-3396 (1991). These mutations produce viral variants which can undergo immune selective pressures in the infected host. The selective pressures favor the outgrowth of those viral variants poorly neutralized by the anti-viral antibodies concurrently present in the host. Therefore, the less diverse the neutralizing response to the infecting virus, the more easily viral escape occurs through random mutations within neutralization epitopes. Since random mutations cannot be anticipated by the immune system, adaptation of the immune response lags behind the virus resulting in chronic infection.
Mutating viruses also exploit a phenomenon known as “original antigenic sin”, wherein the immune system commits itself to responding to the viral variant initially present and continues to make antibodies against the image of this virus variant even when the virus present has effectively shed that image (Webster, J. Immunol. 97:177-183 (1996)). although some level of cross-reactivity with emergent viruses may explain persistence of the seminal antibodies, the mechanism which stops the immune system of the infected host from producing high affinity neutralizing antibodies against emergent viral variants is not clear.
In the case of HIV infection, “original antigenic sin” manifests as B cell clonal dominance, where the original responding B cells are “locked in” through a process termed “deceptive imprinting” or a repertoire freeze” (Kohler et al., Immunol. Today 15:475-478 (1994). This clonal dominance involves restricted diversity in the set of antibodies produced against HIV and apparently can weaken the adaptation of the immune response to emerging mutants and favor viral persistence. In addition, clonal dominance has been associated with the expression of a common idiotype on anti-HIV antibodies with different specificities (Kohler et al., Immunol. Today 15:475-478 (1994); Kohler et al., Immunologist 3:32-34 (1995)). Expression of a common idiotype on antibodies against a particular antigen may therefore be associated with a narrow antibody response against that antigen.
Antibodies with common patterns of auto-reactivity have also been found to have emerged in other chronic inflammatory conditions including HIV, systemic lupus erytnematosus (SLE), graft-versus-host disease, and lepromatous leprosy (Grant et al., J. Immunol. 144:1241-1250 (1990)). this has suggested that the immune system is predisposed to respond along certain autoreactive axes when chronically stimulated by an antigen. There has been speculation that chronic pathogens can selectively activate responses along auto-reactive axes to divert the immune system from mounting a more effective anti-microbial response. If true, there can be therapeutic value in steering the immune response in an infected host away from producing antibodies specific for epitopes delineated by such fruitless axes.
An idiotope common to more than one type of HIV-1 antibody has been discovered (U.S. Pat. No. 5,849,583, incorporated herein by reference in its entirety). The idiotope is common to antibodies produced by restricted B cell clones and has been found to be specifically reactive with at least three anti-HIV antibodies having separate specificities. One particular anti-idiotypic antibody reactive with this idiotope is the mureine monoclonal antibody 1F7. To date, the 1F7 idiotype has been found on antibodies against 2 chronic pathogens, HIV and SIV, suggesting that both selectively activate antibodies along a particular idiotype axis or that chronic stimulation itself drives selection of the 1F7 idiotype. Since uninfected volunteers receiving HIV gp120 vaccination express the 1F7 idiotype on their anti-HIV antibodies, the idiotype appears to be selected in the initial response to HIV and to persist throughout infection.
In the SIV model of HIV infection, administering 1F7 to SHIV-infected animals expressing the 1F7 idiotype on their anti-SHIV antibodies “thawed” the frozen B cell repertoire. Relief from clonal dominance was illustrated by a broadening of the HIV neutralizing antibody response to encompass viruses distinct from the inoculating strain together with an increase in neutralization titer against the inoculating strain.
Shared idiotypic determinants on antibodies reflect genetic relatedness between variable (V) gene segments, common antigenic specificities or overlapping idiotype-based immunoregulatory pathways. The anti-idiotypic antibody 1F7 has been identified to recognize antibodies against different HIV and SIV proteins in approximately 70% of HIV-infected humans and SIV-infected macaques. As the 1F7 idiotype is neither restricted to antibodies expressing the same heavy chain V gene family, nor to antibodies recognizing structurally homologous antigens, it was proposed that antibodies against distinct antigens of chronic pathogen(s), such as HIV, HCV and related disease causing agents, are selected for expression of a common regulatory idiotypic target. The idiotypic linking of antibodies against multiple epitopes of a chronic pathogen can increase the efficiency of immune regulation and limit idiotypic gridlock that might arise from chronic antigenic stimulation.
The presence of 1F7 idiotype on such a diverse set of antiviral antibodies illustrated that B cells expressing Ab2 recognizing the 1F7 idiotype had very high connectivity within the B cell repertoire. Such high connectivity would tend to suppress activation of the regulatory Ab2-bearing B cells and favor assumption of clonal dominance by the responding 1F7 idiotype+ B cells.
A somewhat analogous situation was previously reported with regard to the 16/6 idiotype, which unlike 1F7 is associated with a particular heavy chain V gene family. The 16/6 idiotype was first defined on a monoclonal anti-DNA antibody and later on other auto-antibodies and anti-microbial antibodies. Expression of this idiotype is associated with systemic lupus erythematosus (SLE) in humans and injection of antibodies bearing this idiotype into mice induced SLE-like symptoms. Pathogenic immune complexes in both situations contain 16/6 idiotype+ antibodies, fueling speculation that 16/6 can act as a pathogenic idiotype to perturb the regulatory network in such a way as allows autoimmunity to develop.
However, the probability of chronic pathogens evolving determinants on so many individual proteins to take advantage of this structural feature of B cell networks seems remote. One alternative possibility is that the initial antibody response to HIV gp120 represents a special case, by virtue of gp120 acting as a B cell super-antigen. Investigators showed that gp120 binds a broad set of immunoglobulin molecules based on the heavy chain V gene family expressed. Such polyclonal activation would assure activation of clones expressing the 1F7 Idiotype and the high connectivity of the potential regulatory anti-idiotype would free the 1F7+ B cells to establish clonal dominance.
This proposed pattern of idiotypic focusing could have adaptive as well as negative implications for the immune system. While freezing potential neutralizing antibody responses against a mutating pathogen is clearly a disadvantage, localizing chronic B cell activation within a limited region of idiotypic space could protect against immunopathology and leave a more extensive B cell repertoire free to respond against unrelated pathogens. It remains to be determined how widespread 1F7 idiotype expression is on antibodies against other chronic pathogens and on autoantibodies.
What is needed in the art are additional methods for diagnosis, monitoring and treatment of Hepatitis C virus related disease which improve the immunologic response to the variations in the infectious variant and prevents chronic infection.